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| author | Oleg Nesterov <oleg@redhat.com> | 2010-05-26 14:43:16 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2010-05-27 09:12:46 -0700 |
| commit | ea6d290ca34c4fd91b7348338c0cc7bdeff94a35 (patch) | |
| tree | 6e9bd367650d9233c5b6cf1059845f17cb1bc460 /kernel/fork.c | |
| parent | 4dec2a91fd7e8815d730afbfdcf085cbf53433ac (diff) | |
| download | lwn-ea6d290ca34c4fd91b7348338c0cc7bdeff94a35.tar.gz lwn-ea6d290ca34c4fd91b7348338c0cc7bdeff94a35.zip | |
signals: make task_struct->signal immutable/refcountable
We have a lot of problems with accessing task_struct->signal, it can
"disappear" at any moment. Even current can't use its ->signal safely
after exit_notify(). ->siglock helps, but it is not convenient, not
always possible, and sometimes it makes sense to use task->signal even
after this task has already dead.
This patch adds the reference counter, sigcnt, into signal_struct. This
reference is owned by task_struct and it is dropped in
__put_task_struct(). Perhaps it makes sense to export
get/put_signal_struct() later, but currently I don't see the immediate
reason.
Rename __cleanup_signal() to free_signal_struct() and unexport it. With
the previous changes it does nothing except kmem_cache_free().
Change __exit_signal() to not clear/free ->signal, it will be freed when
the last reference to any thread in the thread group goes away.
Note:
- when the last thead exits signal->tty can point to nowhere, see
the next patch.
- with or without this patch signal_struct->count should go away,
or at least it should be "int nr_threads" for fs/proc. This will
be addressed later.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Alan Cox <alan@linux.intel.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <peterz@infradead.org>
Acked-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel/fork.c')
| -rw-r--r-- | kernel/fork.c | 23 |
1 files changed, 16 insertions, 7 deletions
diff --git a/kernel/fork.c b/kernel/fork.c index b7879ef6e7cd..e08e3012cd6b 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -165,6 +165,18 @@ void free_task(struct task_struct *tsk) } EXPORT_SYMBOL(free_task); +static inline void free_signal_struct(struct signal_struct *sig) +{ + thread_group_cputime_free(sig); + kmem_cache_free(signal_cachep, sig); +} + +static inline void put_signal_struct(struct signal_struct *sig) +{ + if (atomic_dec_and_test(&sig->sigcnt)) + free_signal_struct(sig); +} + void __put_task_struct(struct task_struct *tsk) { WARN_ON(!tsk->exit_state); @@ -173,6 +185,7 @@ void __put_task_struct(struct task_struct *tsk) exit_creds(tsk); delayacct_tsk_free(tsk); + put_signal_struct(tsk->signal); if (!profile_handoff_task(tsk)) free_task(tsk); @@ -864,6 +877,7 @@ static int copy_signal(unsigned long clone_flags, struct task_struct *tsk) if (!sig) return -ENOMEM; + atomic_set(&sig->sigcnt, 1); atomic_set(&sig->count, 1); atomic_set(&sig->live, 1); init_waitqueue_head(&sig->wait_chldexit); @@ -889,12 +903,6 @@ static int copy_signal(unsigned long clone_flags, struct task_struct *tsk) return 0; } -void __cleanup_signal(struct signal_struct *sig) -{ - thread_group_cputime_free(sig); - kmem_cache_free(signal_cachep, sig); -} - static void copy_flags(unsigned long clone_flags, struct task_struct *p) { unsigned long new_flags = p->flags; @@ -1248,6 +1256,7 @@ static struct task_struct *copy_process(unsigned long clone_flags, } if (clone_flags & CLONE_THREAD) { + atomic_inc(¤t->signal->sigcnt); atomic_inc(¤t->signal->count); atomic_inc(¤t->signal->live); p->group_leader = current->group_leader; @@ -1294,7 +1303,7 @@ bad_fork_cleanup_mm: mmput(p->mm); bad_fork_cleanup_signal: if (!(clone_flags & CLONE_THREAD)) - __cleanup_signal(p->signal); + free_signal_struct(p->signal); bad_fork_cleanup_sighand: __cleanup_sighand(p->sighand); bad_fork_cleanup_fs: |